Question: Which of the following numbers is a factor of 90? ${8,9,11,13,14}$
Solution: By definition, a factor of a number will divide evenly into that number. We can start by dividing $90$ by each of our answer choices. $90 \div 8 = 11\text{ R }2$ $90 \div 9 = 10$ $90 \div 11 = 8\text{ R }2$ $90 \div 13 = 6\text{ R }12$ $90 \div 14 = 6\text{ R }6$ The only answer choice that divides into $90$ with no remainder is $9$ $ 10$ $9$ $90$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $9$ are contained within the prime factors of $90$ $90 = 2\times3\times3\times5 9 = 3\times3$ Therefore the only factor of $90$ out of our choices is $9$. We can say that $90$ is divisible by $9$.